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Posts Tagged ‘antenna’

If you were around in the mid 70s in the United States you’d have to have been living under a rock not to know about the great citizen band radio craze made popular by the smash hit “Convoy” by C.W. McCall. If you were into citizen band radio at all you knew that there was a certain prestige to having certain kinds of antennas, especially if you had a CB setup in your home.

For the mobile units, the ones that were installed in your motor vehicle, the antennas were rather simple and relatively weak. They could only send and receive a short distance depending on the time of day. In the afternoon, mobile CB antennas were lucky to reach a few miles, especially during sun spot time. At night, if you were lucky you could reach about 10 to 20 miles, maybe sometimes a little more.

Mobile antennas came in several types. One of the most popular antennas was the fiberglass model that hooked on the back bumper. These antennas were very good transmitters and receivers. Most were about 3/8 of an inch in diameter and about 2 feet tall. Some could handle up to 1000 watts of transmission power.

Another popular type of Mobile Antenna was the magnetic roof top antenna. These were not very powerful but they were real easy to hook up. Just pop the cable into your CB, which was installed usually under the dashboard in your car, and then just take the antenna, stick it out your window and pop it on your roof top. The magnet was strong enough that there would have to be a hurricane for that thing to blow off. These antennas could handle about 300 watts of power which made them a pretty low end antenna for CB use, but they were also very cheap.
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It’s probably not something many people are interested in unless they’re some kind of an electrical engineer or just bored, but understanding how an antenna works can be useful when the one on your TV or radio goes south on you and the reason is beyond your comprehension.

Trying to explain how an antenna works in simple English is not an easy task as there are a lot of technical specifications that need to be explained. But a general understanding is possible without getting into tech speak that would make Einstein cringe.

In order for an antenna to work it has to radiate. Your antenna, whether TV or radio has what is called free electrons running through it. It is these free electrons that vibrate. The question becomes, how do these free electrons vibrate and what causes them to vibrate?

Well, in real life it takes an electric field to move an electron. If you take an isolated straight dipole, the power comes from the combined fields of all the charged particles, both positive and negative, in the antenna. We’ll call this field the antenna’s coulomb field.

In addition to this field, the antenna exhibits a magnetic field that is the sum of the magnetic fields of all the free moving electrons. The antenna also has a dynamic electric field that is the vector sum of the dynamic electric fields of all the free electrons. What we can do is separate the electric field of the antenna at any point in space into two components. One of the components will be in phase with the total magnetic field and the other will be 90 degrees out of phase. The in-phase component is the radiation field of the antenna and the out of phase component is the induction field. At the antenna, both fields are parallel to the metal surface.
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Continuing with our research into the CB craze of the mid 70s we’ll take a look at what were considered the elite antennas when it came to having a CB setup. While the truckers may have ruled the roads and channel 19, it was the everyday hobbyist who ruled the airwaves from his home, and rule they did.

If you were on CB and really wanted to impress people with your booming voice over the airwaves you had no choice but to set up a base unit. Not only were the units themselves powerful but the antennas that people put up on their roof tops could have given some rival TV stations a run for their money.

Choosing a CB antenna for your base station was not easy. There were plenty to choose from and they all had their pluses and minuses.

One of the most powerful, yet most frustrating was the ever popular Moon Raker. This was a beam antenna that looked very similar to TV antennas, most having 3 elements mounted on an 11 meter base. These were called regular Moon Rakers. However, there were beam antennas that had up to six elements on them. They were referred to as a Moon Raker 6. These things were huge. The problem with them was that they were directional antennas. What this means is that depending on what direction your antenna was pointing that was where you got your best reception and transmission. So if you were speaking to somebody who was south of you and your antenna was pointing north you had to turn the antenna 180 degrees in order to get a decent reception. This got to be a pain after a while. The plus side was that these antennas were so powerful they could cut through anything once you had your target zeroed in.
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